Lift mechanism



June 1965 J. c. CHRISTENSON 3,187,911

LIFT MECHANISM Filed June 27, 1962 4 Sheets-Sheet 1 FIG. 2

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i I 4o 40 I :h 25 22 I I4 A l as A M l8 I 4 U f I r r L I l4 l6 \5 IO 17 2o 20 I7 4 INVENTOR JOHN C. CHRISTENSON ATTORNEY J. C. CHRISTENSON June 8, 1965 LIFT MECHANISM 4 Sheets-Sheet 2 Filed June 27, 1962 INVENTOR JOHN C. CHR|STENSON ATTORNEY n 8, 1965 J. c. CHRISTENSON LIFT MECHANISM 4 Sheets-Sheet 3 Filed June 27, 1962 INVENTOR JOHN C. CHRISTENSON BY/K ATTORNEY June 8, 1965 J, c. CHRISTENSON 3,187,911

mrruncmrsu Filed June 27, 1962 4 Sheets-Sheet 4 FIG.7

mvsmon r JOHN c. CHRISTENSQN;

ATTORNEY United States Patent 3,187,911 LIFT MECHANISM John C. Christensen, Battle Creek, Mich., assignor to Clark Equipment Company, a corporation of Michigan Filed June 27, 1962, Ser. No. 205,605 21 Claims. (Cl. 214-140) This invention relates to lift or elevator mechanisms, and more particularly to a folding upright construction for lift trucks and the like.

Since the advent of lift trucks and other operator driven devices utilizing upright elevator mechanisms for engaging, elevating and transporting loads from one location to another, it has been a primary objective to achieve a combination of functional and structural advantages which include (1) the capability of elevating a load on load engaging means, such as fork tines, from a ground level position wherein the upright is at a relatively low collapsed height to a position of relatively high elevation; (2) to design an upright construction which provides maximum operator visibility through the upright; (3) to design a relatively economical and simple construction which is low in maintenance cost; (4) to minimize the weight of the upright mechanism and load which overhangs the front axle of a lift truck, for example, so as to effectively increase load lifting capacity of the truck for a given total truck weight; and (5) to provide a substantially straight line vertical lift of the load engaging means while at the same time providing a stable upright mechanism which is supported by the truck. Many attempts have been made heretofore to provide load elevating mechanism capable of achieving to a significant degree the above combination of objectives, but, to my knowledge, none have succeeded to the extent achieved by the present invention.

In achieving the aforementioned combination of objectives, and in carrying out the present invention I have devised an extremely novel structure which utilizes a folding upright concept in which a double parallelogram linkage mechanism straddles side portions of the truck, which collapses to a height which is well below the line of sight of an operator, and which in elevation provides a picture window visibility through the upright. One of the pairs of parallelogram linkages straddling portions of the truck longitudinally thereof is secured at its one ends to the forward end of the truck, and the other pair of such linkages is secured at the other ends to the opposite ends of the first-mentioned pair of linkages. The load engaging or fork mechanism is secured to the opposite ends of the second-mentioned parallelogram linkages.

The pairs of such linkages are connected together through I the truck chassis, at the connected ends thereof, and by the load engaging means to provide lateral rigidity. A pair of hydraulic lift cylinder is provided on each side of the truck, one being connected between diagonally related corners of each second-mentioned linkage means and the other being connected to the truck and to the rear end of each first-mentioned linkage. These lift cylinders operate in sequence to elevate the folding upright from ground level to a position of relatively high elevation by first elevating the second-mentioned linkages to a position of intermediate elevation, and then simultaneously elevating both pairs of said linkages to maximum elevation wherein the fork is located .at the uppermost elevation of the secondmentioned pair of linkages. Substantially straight-line elevation of the fork is achieved by a unique use of servo valve means operative between and controlled by the movement between the pair of parallelogram linkages on each side of the truck, which movement controls the valve means in such a manner as to coordinate the truck mounted lift cylinders therewith which function in turn as follow-up actuators for the servo valve mechanism.

My invention is designed such that the substantially straight line vertical motion occurs with the load engaging means located immediately adjacent the front wheels of the truck, while substantially the entire parallelogram linkage and associated mechanism is located rearwardly of the front axle of the truck, whereby to maximize longitudinal stability of the truck. In addition, means is provided in association with the second-mentioned pair of said linkages for tilting the fork either forwardly or rearwardly of a level position.

In accordance with the foregoing, it is one of the primary objects of the present invention to provide an upright for lift trucks, and the like, which is collapsible to a very low height while being actuatable to a relatively high elevation.

Other important objects are to provide a novel folding or collapsible upright for lift trucks, and the like, as well as an upright structure in which the center of gravity is located rearwardly of the front axle of the truck.

Another important object of the invention is to provide an upright for lift trucks, and the like, which affords a high degree of operator visibility therethrough at all times during raising and lowering movement thereof.

An additional object of the invention is to provide a generally improved and novel load lifting means for use with lift trucks, and the like, of relatively economical and simple construction.

A further object of the invention is to provide a load lifting mechanism of the type contemplated wherein control means operates to maintain substantially straight line vertical movement of the load engaging means during a significant portion of the total elevation of the load engaging means.

Other objects, features, and advantages of the present invention will become apparent to those skilled in the art in view of the following description taken in conjunction with the drawings, wherein:

FIGURE 1 is a view of my invention in side elevation mounted on a lift truck and shown in positions of minimum and maximum elevation;

FIGURE 2 is a front view of the structure shown i FIG. 1 with the upright mechanism illustrated at a position of maximum elevation;

FIGURE 3 is a somewhat enlarged and schematized showing of the invention taken along lines 44 of FIG. 2 and showing the upright mechanism in three positions of elevation;

FIGURE 4 is an enlarged plan view of the side of the truck shown in FIG. 1 with the upright mechanism in a folded or collapsed position;

FIGURE 5 is a detail side view of control valve means in the upright which operates to provide straight line motion of the load engaging means;

FIGURES 6A, 6B and 6C comprise a diagrammatic illustration of the three operating positions of the control valve means of FIG. 5;

FIGURES 7 and 8 are detail views of certain of the connections of linkages, cylinder actuators and the like utilized in my invention; and

FIGURE 9 is a plan view of the upper portion of the means shown in FIG. 5.

Referring now in detail to the drawing, a lift truck chassis of generally conventional construction is shown at numeral 10 and comprises a pair of longitudinal transversely spaced frame members 12 connected together at the rear end thereof by a transverse counterweight member 14 having a pair of rear steer wheels 15 mounted on a steer axle 16 which is pivotally supported in known manner from the truck frame by a trunnion, not shown, the front end of the framework being pivota'lly supported from a transverse rigid drive axle housing 17 by ring members 18 journaled on the drive axle housing, and outwardly projecting elements 19 bolted to members ltd and connected, as by welding, to frame members 12. Forward drive wheels 2% are mounted at the ends of the drive axle; An upwardly and forwardly extending plate section 21 is provided at each side frame member 12. it extends over the outer side of the adjacent drive wheel for supporting the upright assembly of thisinvention. An opera-tors station is mounted'centrally of the truck and comprises generally a steering wheel 22 mounted on a steering post 23 which extends through a door board section 2 4, the steering wheel being suitably connected to the steer axle 16 by a conventional steering gear. The various controls for operating the truck, including transmission and brake controls, and valve controls for operating the upright, are conventional and have not been illustrated. An operators seat :25 is mounted atop an engine compartment 25 which extends laterally of the truck to a location inside the linkage'mechanism of the upright, described below, on either side of the truck. The cover assembly of the engine compartment is supported from an elongated transverse frame supported plate member 27 which extends forwardly from the counterweight 14 and includes floorbo-ard which flares inwardly from plate 27 to provide an elongated space 2.9 forwardly of each side of the truck and inside of the upright mechanism as best shown in FIG. 4. An elongatedslot 28 is provided in plate member 27 adjacent each .side of the truck for a purpose which will appear below.

The upright assembly which comprises my invention is shown generally at numeral 30; it is mounted pivotally from thefront' end of the truck inwardly of parallel frame members 12 and extends diagonally rearwardly thereof abovevplate members 27, being supportedat the rear end bya pair of transversely spaced lift cylinders 32 which extend through slots 23in plate section 27, opposite sides of the uprightassembly being located in straddling relation to engine. compartment 26 and connected together by transverse bar members, or the like, as required to stabilize and synchronize movements of the opposite side assemblies of the upright. It will be appreciated that the upright mechanism on each side of the truck is duplicated on the opposite side thereof, being secured together by the chassis of the truck and by transverse shaft means between parts of the upright mechanism to be described, while the fork tines or other load engaging means is suitably supported from and between the side assemblies of the upright at the front end of the truck. The following description'taken injconjunction with the drawing will be related primarily to the upright construction on the right side only of the tr-uck,.it being understood that such structure is duplicated on the opposite side thereof as shown in FIG. 2. j

The fol-ding uprightfitl comprises generally a first pair of transversely spaced, rearwardly extending parallelogram linkages 40 mounted pivotally inwardly from the front ends of opposite ones of front sections 21 of frame members 12, a second pair of transversely spaced, forwardly extending parallelogram linkages 4-2 mounted transversely inwardly of and from the opposite ends of linkages ,40 and having a load carriage and fork assembly 43 mounted pivotally at the front ends thereof, and a pair of transversely spaced primary hydraulic lift cylinder motors 44 operatively connecting front and rear diagonally related corners of the linkageslZ for actuating fork assembly 43 with linkages 42 to a primary lift position B (FIG. 3) about the rear ends-of linkages 4b, the second pair of lift cylinders 32 being connected pivotally inward- 'ly of the opposite sides of the truck at j and to the movable rear ends of linkages 4% for elevating linkages 4t and 42 together with actuators 44 to a maximum lift position wherein fork assembly 43 is located at elevation C. A pair of transversely spaced servo valve means 49 (FIG. are mounted between adjacent arms of each of the two sets of linkages 40 and 42 and are operable to control the actuation of the linkage system by actuator motors '32 d 1 such that fork assembly 43 is actuated in a substantially straight vertical line between elevations B and C. If desired, one valve means 4% may be used at one side only of the sets of linkages in preference to the use of two such valve means; whether one or a pair of valve means 4 is used is immaterial to the operation of the invention.

Each of the parallelogram linkages MB comprises upper rigid square section link members 5%) and lower rigid thinplate section link m mbers 5-2 below and in the plane of the other side portion of link fill, each pair of links 52 and 5% being connected pivotally to the front end of the truck by a pair of vertically spaced pivot pins a and k, respecpair of links 5b is connected by an upper transverse pivot rod h and links '52 by a lower transverse pivot rod g, each'end portion of rods g and It being connected together by a pair of transversely :spaced vertical links 6 which form with truck supported pivots 0. and k and links -53 and 52 the pair of spaced parallelogram linkages Actuator motor 32 is pivoted at the cylinder base end thereof inwardly of the'lower portion of each frame member 12 on a cantilevered pivot pin 1' and extends upwardly therefrom through slot 23, the piston rod end being pivotally connected to rod g transversely inside of link '52 and vertically below link 5%) (FIG. 7).

Each parallelogram link-age assembly 42 comprises a pair of parallel, vertically spaced, forwardly extending link rods 7t) and 72 pivotally supported between links 64 from rods g and h, respectively, transversely inwardly of rods 5b and 52, theforward ends thereof being pivotally connected to a pair of vertically spaced pivot pinsb and c which are preferably coaxial with pins a and k, respectively, when the upright assembly is in fully retracted or lowered position A. Link rod 72 is shown as having a circular section and is connected to transverse rod 11 immediately adjacent inner link as, rod 72 overlying rod '76 and being pivotally connected at the forward end thereof to pivot pin 0. Link rod 70 includes a bifurcated rear end rod portion 75 which extends forwardly and is rigidly secured to the base end. of a hydraulic tilt cylinder '76 having a piston rod '78 pivotally connected to pin b. Link rod 7d extends through opening 2? formed between floorboard 24- and each frame member 12, said opening permitting pivotal movement of said link rod as i-t is actuated upwardly'from position A of the upright assembly. Connected between each corresponding pair of pivot members 0 and g is a primary lift cylinder assembly 8d the piston rod 82 of which is pivotally mounted on pin c, the base end of the cylinder being rigidly supported from the end of a rod '84 which is pivotally mounted on rod g and which is adapted to move through the slot of the bifurcated end 75 of link rods 7th duringelev-ation of the upright. Pivot pins 11 and c (and also pins 11 and k) are spaced vertically a distance equal to the spacing of rods g and h, whereby to form with link rods '76? and '72 the second pair of parallelogram linkages 42 when cylinder motor 76 is retracted to locate pins]; and c in vertically spaced relation.

Fork assembly 43 is supported from each pair of pins 1) and c at each side of the truck by means of a pair of vertically extending, transversely spaced plate members so which connect opposite end portions of said pivot pins and which are secured, as by welding, to a pair of transversely extending, vertically spaced fork bar members 92, from which are supported by bracket portions 94 a pair transversely spaced L-shaped fork tines 96. Recesses 98 are formed in the upper and opposite side portions of counterweight 14 (FIGS. 1 and 4) to provide space for movement of certain links of the upright assembly when it is retracted from an elevated position.

Referring especially to FIGS. 5, 8 and 9, valve mechanism 4-9 is provided to confine the movementof fork assembly 43 between elevated positions B and C to a substantially straight line vertical path. An auxiliary valve housing 100 is secured rigidly to each of the inner ones of pairs of links 64 and contains a three-position spool valve and suitable porting of conventional design, not shown, the spool valve being actuated by a reciprocable valve stem 102 which is secured pivotally at a pin i intermediate the ends of a link 104. The link 104 is pivotally mounted on rod h at the one end and connected for sliding movement through a forwardly spaced block I from the opposite sides of which project pins 1' to which are pivot'ally connected the ends of a pair of links 106 and 108 of equal length which extend diagonally rearwardly in diverging relation, being pivoted at pins 0 and n to links 72 and 50, respectively. Each pair of links 106 and 108, as connected, comprises a toggle. Movement of the upright assembly from fork location A to fork location C varies the angle of the toggle oln so as to slidably project link 104 forwardly through block I and simultaneouslypivot the link about rod h which actuates spool valve rod 102 to various valve control positions, as shown in FIGS. 6A, 6B and 6C, as will be described in detail below.

A pump, not shown, is adapted to supply pressure fluid to valve 100 through a conduit 110, the valve 100 directing the flow, depending upon the position of control rod 102, through valve porting to the cylinder and sump (FIG. 6A) when angle lhg between links 104 and 64 is less than 90, to the sump through conduits 110 and 112 with a column of oil locked in cylinder 80 when said angle is equal to 90 (FIG. 6B), and to the base only of cylinder 80 when said angle is more than 90 with both the cylinder ports and the pump ports to the sump closed (FIG. 6C). The manner in which control valve 49 operates in conjunction with the lift cylinders to control the path of movement of fork assembly 43 .during elevation and lowering will be described below. In the interests of clarity valve mechanism 49 is not illustrated in FIGS. 2 and 4.

Operation A driver of truck 10 may most readily mount the truck for operating the same from the front end thereof by stepping up on fioorboard 24 over axle 17 and thence around one side of steering wheel 22 to seat 25 between the parallelogram linkage assemblies 40 and 42 whether the fork assembly 43 is located at position A or between positions B and C. With the operator in position on seat 25 and the upright assembly in position A, the complete upright assembly is located in the solid line position This design greatly facilitates safety in operation of the; truck by providing maximum visibility from the truck both of the load and the area in which the truck is being operated. Also, it will be noted that the center of gravity of the mass of the upright mechanism is located a substantial distance to the rear of axle 17 which facilitates the use of a truck of shorter wheel base, and therefore shorter turning radius, as compared with present day lift trucks of given load capacity, or, to express it in another manner, my design effectively increases the load lifting capacity of the truck for a given total truck weight. In effect, therefore, the maximum forward tipping moment of the truck may be utilized for handling a load on fork 96, so that the load which can be carried on the fork is correspondingly increased.

Control levers, not shown, may be conveniently located at the operators station for manually controlling the pair of lift cylinders 44 and fork tilt cylinders 76. If desired, the operator may actuate tilt cylinders 76 to extend piston rods 78 whereby to cause the fork assembly to be rotated to a rearward tilt position about pivot pins c, or piston rod 78 may be retracted a small amount to provide forward tilt of forks 96 about pins 0. With fork 96 in a level position as shown, linkage assemblies 42 form two transversely spaced parallelograms, and primary lift cylinders 89 may be actuated to extend piston rods 82 which actuates linkage assemblies 42 with fork assembly 43 along an arcuate path 116 to elevation B, the lifting moment being imposed, of course, about pivot rod h and a slightly arcuate motion of the assembly from position A to position B being imposed by link rods 72 with linkage assemblies 42 maintaining the fork assembly in a level position. during such elevation linkage assemblies 40 remain in the initial positions thereof, while linkage assemblies 42 are rotated about pivot rods 11 and g to position pivot pins b and c in positions b and c, as shown in FIG. 3.

To elevate the fork from position B to position C the.

manual control valve is positioned to continue to direct pressure fluid to primary lift motor 44 to extend further the piston rod 84 which causes valve assembly 49 to be controlled automatically as a function of the changing relationship of the linkage means (FIG. 5) described above, whereupon secondary cylinder assemblies 32 are energized by the operation of valve assembly 49 to extend the piston rods thereof. Continuation of extension of cylinder motors 32 causes link rods 50 and 52 of linkage assemblies 40 to be actuated about. truck supportedpins a and k from the initial position thereof to the position indicated in FIG. 3 in which the pivot rods h and g are located at positions h" and g" respectively, while each cylinder assembly 32 pivots forwardly in a clockwise direction about pin i from its initial rearwardly diagonally extending position to a slightly forwardly extending position. Such actuation of the complete upright assembly by the conjoint action of cylinder motors 32 and 44 causes the fork assembly to be actuated in a substantially straight vertical path from position B to position C, as indicated at numeral 120, as a result of the coordinating operation of valve assembly 49 which functions to control further extension of primary lift cylinder motors 44 in coordination with extension of lift motors 32 such that parallelogram linkage assemblies 42 are actuated with clockwise pivotal movement of linkage assemblies 40 from the geometric disposition thereof at elevation B to the geometric disposition illustrated at maximum elevation C.

The operation of valve assembly 49 will now be described.

During the movement of linkage assembly 42 from ground level position A to elevated position B an anglev ohm is produced at position B between links 50 and 72, said links along with toggle 106, 108 andmember 104 being coplanar in a direction transverse of the truck when fork assembly 43 is at position A. During this movement between positions A and B valve actuating arm 104 causes the spool valve in valve housing 100 to assume and remain in a position in which it by-passes hydraulic fluid from the pump back to the sump, as illustrated in FIG. 6A, thus permitting cylinder motor 32- to remain in its collapsed position. In other words, the valve is located in an open-center position in communication with both cylinders 32 and the sump. At position B arm 104 is substantially perpendicular to arm 64, but so long as arm 104 forms an angle of less than with link 64,

which is the 'case between positions A and B, the valve remains in the position of FIG. 6A. Withvalve 100 located as in FIG. 6A no flow of hydraulic fluid is directed to the cylinder 32 which will cause to extend, and since the piston rod of cylinder 32 is in a fully retracted position it cannot move in either direction, thus permitting cylinder motor 44 to actuate linkage assembly 42 alone in both elevation and lowering movement between positions A and B. i

As lift cylinder 44 is further extended to actuate fork assembly 43 above position B it will be apparent that pivot c tends to continue its previous arcuate travel about pivot h. However, any increase of the angle formed between the arms connecting points I, h and g in excess of 90 imparts suflicient additional linear motion to the valve 100 so that the valve connects the valve ports to supply oil to the base of cylinder 32 as in FIG. 6C which causes pivots g and h to move arcuately about their respective pivot pins and k, which motion tends to decrease angle lhg until ithas again assumed the magnitude of a right angle. Whenever angle lhg is a right angle the valve spool is located to effect a connection of the pump to the sump, as shown in FIG. 6B, which locks fluid in the base of cylinder motor 32, which is the condition illustrated in FIG. 3 at position B. Thus, with each additional increment of lifting motion of fork assembly 43 by lift cylinders 44 in elevation above position B the operation of servo valve assemblies 49 cause cylinder motors 32 to function as a follow-up piston motor compensating through the-operation of linkage assemblies the tendency of linkage assemblies 42 to force the fork assembly to move in an arcuate path. The entire double parallelogram linkage assembly with the coordinated operation of lifting motors 32 and 44 therefore tends to elevate the fork assembly 43 in increments, in effect, in a substantially straight vertical line between positions B and C as arm 104 tends to be cyclically actuated relative to arm 64 between an angle of 90 and an angle slightly in excess of 90, thereby alternately actuating valve 100 through arm 102 between the positions shown in FIGS. 6B and 6C which continuously reacts upon cylinder motors 32 to compensate, as aforesaid, the tendency of cylinder motors 44 to cause areuate motion of the fork assembly above position B. In other words, it will be seen that any deviation of arm 104 in excess of a right angle relationship to arm 64 actuates valve 100 so as to re-' establish the right angle relationship between arms 104 and V returns valve 100 to the FIG. 6B position. Continuation of the alternating movement of valve 100 between the positions of. FIGS. 6A and 6B thus coordinates the .operation of lift cylinders 32 and 44 t-oproduce substantially straight verticalmovement of fork assembly 43 from position C to position B.

The above-described control of flow through valve 10%) is readily accomplished, of course, by a suitable arrangement of the porting within the valve housing such that the valve spool connects the ports during actuationv thereof as aforesaid to effect the various operating conditions illustrated diagrammatically in FIGS. 6A, 6B and 6C.

It will be appreciatedrthat the hydraulic actuating circuit which includes lift cylinders 32 and 44, control valve 100 and the interconnections thereof may preferably and readily be designed to provide a continuously smooth elevating movement of the fork assembly be' tween positions B and C, as distinguished from the incrernental'rnovement above .described in connection with the operation of valve assembly 49. The. foregoing described cyclical operation of the valve assembly 49 is not as desirable in actual practice as is a continuously smooth elevating movement because of the tendency to induce somewhat 'jerky operation of the fork assembly between positions B and C. The foregoing incremental mode of operation of the valve assembly 49 is set forth in iletail not only to provide a description of one feasible mode of operation, but also to clarify the particular'relationships involved of the links, valve assembly and lift cylinders as they cooperate to elevate'the fork assembly in a substantially straight line between positions B and C. Alternatively, as mentioned above, various design criteria are available to assure, if desired, that secondary lift motors 32 continuously lag by a small amount primary lift motors 44 during such elevation'such that valve 100 remains continuously partially open (FIG. 6C) for allowing a continuous flow of oil to the secondary lift motors 32 in the proper proportion to maintain a vertical lift between positions B and C. To assure this result is merely a 'motors 44 and the desired restriction to lift motors 32 is provided by valve ltlfiwhich is preferably of a feathering or modulating type such as produced by Vickers, Inc., Division of the Sperry Rand Corporation, Detroit, Michigan, Vickers Valve Model CM 11. In such a design, valve 100 remains feathered open throughout elevating movement between positions 'B and C with lift motors 32 continuously lagging extension of .lift motors 44 which produces continuous, non-incremental and substantially vertical movement of the fork assembly between said positions, whether the fork assembly is being elevated or lowered;

It will be appreciated that the relatively small arcuate movement of the fork assembly between positions A and B is' quite acceptable in lift truck practice, first because the "increase in the distance between the center of gravity of a load and the front axle of the truck-may be reduced to a relatively small value, and secondly because at the relatively low elevation up to position B the stability of the truck will be as good as or better than the stability of maximum lift position C under any given fork loading condition. Also, inasmuch as only the fork assembly is capable of lifting by. means of operation of cylinder motor 70, overall stability of the upright assembly is improved as compared with modern lift truck practice wherein in order to tilt the fork assembly it is usually necessary to tilt in a forward direction the entire upright assembly thereby causing a greater decrease in truck stability than in the present invention. 7

Although'only one embodiment of my invention has been illustrated and described in detail, it will be apparent to those skilled in the art that various changes and modifications in the structure and relative arrangement of parts may be made to suit individual requirements without departing from the scope of the invention. I claim:

ll. In combination with a lift truck, first parallelogram linkage means pivotally supported from the front end of the truck and'extending longitudinally rearwardly, second parallelogram linkage means pivotally supported from the rear end of said first linkage means and extending forwardly, load engaging means'pivotally supported from the front end of said second linkage means, a first cylinder-piston means connected between diagonally related corners of said second linkage means operable to swing said second linkage means about its connection to said first linkage means,-a second cylinder-piston means pivotally supported from the truck and connected adjacent the rear end of said first linkage means and operable to pivot said first linkage means about its truck support whereby to raise and lower conjointly said first and second linkage means, a source of pressure fluid and control valve means operatively connected to said first and second linkage means and responsive to variations in the angle therebetween for connecting and disconnecting said second cylinder-piston means during operation thereof to and from said piston source of pressure fluid while connecting the first cylinder-piston means to said source to coordinate operation of said first and second cylinder-piston means in order to elevate said load engaging means along a predetermined path.

2. An elevating mechanism comprising a base, first and second parallelogram linkage means having common substantially vertical link means and each including parallel links pivotally connected on respectively common axes to said common link means, said parallel links of said first linkage means also being pivotally connected to said base in vertically spaced relation, load-engaging means having said parallel links of said second linkage means pivotally connected thereto at vertically spaced points and movable thereby between lowered and elevated positions, and means for extending and retracting the linkage means to raise and lower the load-engaging means from and to a lowermost position attained in retracted position of the linkage means, the respective pivotal connections of the parallel links of the first and second linkage means to said base and to said load-engaging means lying on respectively common axes in said retracted position to provide substantially coplanar disposition of the respective links of the linkage means, said extending and retracting means comprising motor means operable to swing the first linkage means relative to the base and to swing the second linkage means on the first linkage means.

3. An elevating mechanism as defined in claim 2,

all directions, and said linkage means in retracted position extend not substantially above the frame to avoid obstruction of said visibility.

4. An elevating mechanism as defined in claim 2, wherein said motor means comprises a first fluid cylinder actuator connected between the first linkage means and the base, and a second fluid cylinder actuator connected between diagonally related corners of the second linkage means.

5. An elevating mechanism as defined in claim 4, wherein said motor means comprises a first fluid actuator operable to swing the first linkage means on the base, and a second actuator operable to swing the second linkage means independently of the first linkage means to raise and lower the load-engaging means between said lowermost position and a primary elevated position, said first and second actuators being operable simultaneously to swing the first and second linkage means conjointly about the respective pivotal supports thereof to move the load-engaging means between said primary elevated position and a higher secondary elevated position.

6. An elevating mechanism as defined in claim 5, including valve means for controlling the actuators, third parallelogram linkage means defined partly by the first and second linkage means and including a pair of togglerelated links, and means connecting said toggle-related links to said valve means for operation thereof in response to variation in the angle defined between the first and second linkage means, said valve means holding the first actuator inactivated while activating the second actuator for said independent swinging of the second linkage means between minimum and maximum angular relation to the first linkage means corresponding respectively to said lowermost and primary elevated positions of the load-engaging means, and activating both actuators for said conjoint swinging of the first and second linkage means while maintaining in predetermined ratio the angular relation of each link means to the horizontal plane of the pivotal connection of the toggle-related links to each other, whereby to restrict loading means movement between said primary and secondary elevated positions to a substantially straight path.

7. An elevating mechanism as defined in claim 6, in which said ratio is 1:1.

8. An elevating mechanism comprising a base, substantially vertical link means, first and second parallelogram linkages each including parallel links pivotally connected to said vetrical links means, said parallel links of said first linkage also being pivotally connected to said base in vertically spaced relation, other substantially vertical link means having said parallel links of said second linkage pivotally connected thereto at vertically spaced points, and motor means for extending and retracting the linkages between a fully elevated position and a fully retracted position and operable to swing said first linkage relative to the base and said second linkage relative to the first linkage, the respective pivotal connections of the parallel links of the first and second linkages to said base and to said other vertical link means lying on respectively common axes in said retracted position.

9. An elevating mechanism as defined in claim 8, wherein at least one of the parallel links of the second linkage means is extensible and retractable for swinging the other vertical link means about the pivotal connection thereof to the other of the parallel links.

10. An elevating mechanism as defined in claim 8, wherein said motor means comprises a first fluid cylinder actuator connected between the first linkage and the base, and a second fluid cylinderactuator connectedbetween diagonally related corners of the second linkage, and including valve means operatively connected to the first and second linkages controlling said actuators in response to movements of the linkages.

11. An elevating mechanism as defined in claim 10, wherein said second actuator is operable to swing the second linkage independently of the first linkage for movement between retracted position and a primary elevated position, and the first and second actuators are operable simultaneously to swing the first and second linkages conjointly about the respective pivotal supports thereof to move the second linkage between said primary elevated position and a higher secondary elevated position.

12. An elevating mechanism comprising a base, first parallelogram linkage means pivotally connected to a forward portion of said base and extending rearwardly therefrom, second parallelogram linkage means pivotally connected to the rear end of said first linkage means extending forwardly therefrom and disposable to define with the first linkage means an angle with its apex at a common pivotal axis and directed rearwardly, and motor means operatively connected to the first and second linkage means for concurrently raising and lowering the forward end of the second linkage means relative to the first linkage means and the rear end of the first linkage means relative to the base and consequently varying said angle, and means responsive to variation in said angle to control the relative rates of movement of the two linkage means for maintaining in a predetermined relation the angles between each linkage means and a predetermined plane through said apex.

13. An elevating mechanism as defined in claim 12,'in which said predetermined plane is substantially horizontal, and the angles between said horizontal plane and each linkage means are substantially equal.

14. An elevating mechanism as defined in claim 12, wherein the linkage means may be lowered to a position in which all of said angles are substantially zero.

15. In combination with a truck having an operators station and a frame completely below the normal viewing level from said station afiording unimpeded visibility at least forwardly, load-lifting mechanism mounted on the truck comprising first and second parallelogram linkages disposed in fully retracted position substantially at the level of said frame in substantially parallel relation, said first linkage including a first pair of parallel link means pivotally connected at vertically spaced points :to the forward portion of the frame and extending rearwardly therefrom, substantially vertical link structure having pivotal connection at vertically spaced points thereon to said first parallel link means, said second linkage including a second pair of parallel link means pivotally connected to said vertical link structure and extending forwardly therefrom, load-engaging means pivotally connected .at vertically spaced points thereon-to the forward ends .of the second pair of parallel link means, and means for extending and retracting said lifting mechanism in two stages comprising v.one stage in whichthe second linkage is swung on the first linkage between said fully retracted position and a primary elevated position, and another stage in which both linkages are swung about the pivotal mounts thereof between said primary elevated position and a higher secondary elevated position, said pivotal connections of the first andsecond pairs of parallellink means being located to effect dispositionof the respective link means .in substantially parallel relation in said retractedposition.

16. A 'lift truck substantially as defined in claim 15, wherein said frame affords substantially unobstructed visibility from said station .in all directions, and .the pivotal connections of both ;pairs of parallel link means to the vertical link structure are on respectively common axes, and the pivotal connections .of the Second pair of parallel links to the load-engaging-means coincide in said retractedlinkage position with the axes of :the corresponding pivotal connections of the first ,pair ofpara'llel link means to the frame, whereby said linkages are dis posed in substantially coplanar relation transversely of g the truck in the retractediposition.

17. A lift truck as defined in claim 15, wherein at least one of the parallel links of thesecond linkage means is extensible and retractable for swinging the load-engaging means about the pivotal connection thereofto the other of the parallel link means.-

18. In combination with a truck having an operators station, a frame completely below the normal viewing level from said station to alfordluriimpeded visibility in all directions, load-lifting mechanism mounted on the truck comprising first and a second extensible :and retractable parallelogram linkages which in fully retracted position are disposed not substantially above said frame and in substantially coplanar relation transversely of the truck, saidfirstI linkage including a first pairiof parallel link meanspivotally connected at vertically spaced points to the forward portion of the frame and extending rearwardly therefrom and also including substantially vertical link means having pivotal connection at vertically spaced points thereon to :said parallel link means, said secondlinkage also including said vertical .link :means and a second pair .of parallel link means pivotally connected to the vertical link means .on the :same axes .as said first parallel link means and :extending forwardly, load-engaging means piv0ta'lly-connected:to theforward ends of the parallel link means 'of the second linkage on axes which in retracted position of the linkages coincide with the axes of the pivotal connections to the frame of the parallel link means of the first linkage, and means for extending and retracting said lifting mechanism.

19. Alift truck as set forth in claim 18, wherein said extending and retracting means comprise first pressure fluid means acting between the frame and the first linkage, and second pressure fluid means acting between diagonally opposite corners of the second linkage, and including valve means controlling said pressure fluid means responsive to simultaneous pivotal movement of the linkages for maintaining the movement of each linkage at a predetermined rate to effect raising and lowering of the load-engaging means in a substantially vertical path.

20. A lift truck as set forth in claim '19, wherein said valve means comprise a third parallelogram linkage defined by a pair of pivotally connected toggle-related links each pivoted to one of the adjacent links of each of the first and second linkages having a common pivotal axis, a valve element, and a valve actuator extending between said element and the pivotal connection to each other of said toggle-related links for moving the valve element in response to variation in the angular relationship of said adjacent links to during simultaneous movement of the first and second linkages maintain substantially in a predetermined relation the angles between said adjacent links and the horizonal plane of said common axis.

21. In combination with a truck having an operators station and a frame below the normal viewinglevel from said station to afford unobstructed visibility at least for- Wardly, load-lifting mechanism comprising first and second extensible and retractable parallelogram linkages disposed not significantly above the frame in retracted position, said first linkage including a first pair of parallel link means pivotally connected to the forward portion of the frame on vertically spaced axes and extending rearwardly therefrom, substantially vertical link means having said parallel link means pivotally connected thereto on vertically spaced axes, said second linkage including a second pair of parallel link means pivotally connected to'said vertical link means on vertically spaced axes and extending forwardly therefrom, load-engaging means pivotally connected on vertically spaced axes to the forward ends of saidsecond pair of parallel link means, and two-stage means for extending and retracting said lifting mechanism operable to move the second pair of link means about its connections to the vertical link means independently of said first pair of link means for moving the forward ends thereof between said retracted postiion and a primary elevated position and to move the first pair of link means about its connections to the frame while contemporaneously moving the second pair of link means for effecting movement of the forward ends thereof in a substantially vertical path between said primary elevated position and a higher secondary elevated position.

References (Jited by the Examiner UNITED STATES PATENTS 2,953,264 9/60 Ulinski 214 '1'30 2,980,271 4/61 Ulinski 2'14 1s0 3,067,887 12/62 Quayle 214 131 HUGO O. SCI-IULZ, Primary Examiner.

UNITED STATES PA'IEINT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,187,911 June 8, 1965 John C. Christenson It is hereby certified that error appears in the above numbered patent reqiiring correction and that the said Letters Patent should read as ooz'rectedbelow.

Column 1, line 47, for "other" read one column 6, line 13, for "during" read During line 67, after "cause" insert it column 8, line 42, for "lifting read tilting column 9, line 2, strike out "piston"; line 32, strike out "above"; column 12, line 48, for "postiion" read position Signed and sealed this 16th day of November 1965.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Altvsting Officer Commissioner of Patents 

1. IN COMBINATION WITH A LIFT TRUCK, FIRST PARALLELOGRAM LINKAGE MEANS PIVOTALLY SUPPORTED FROM THE FRONT END OF THE TRUCK AND EXTENDING LONGITUDINALLY REARWARDLY, SECOND PARALLELOGRAM LINKAGE MEANS PIVOTALLY SUPPORTED FROM THE REAR END OF SAID FIRST LINKAGE MEANS AND EXTENDING FORWARDLY, LOAD ENGAGING MEANS PIVOTALLY SUPPORTED FROM THE FRONT END OF SAID SECOND LINKAGE MEANS, A FIRST CYLINDER-PISTON MEANS CONNECTED BETWEEN DIAGONALLY RELATED CORNERS OF SAID SECOND LINKAGE MEANS OPERABLE TO SWING SAID SECOND LINKAGE MEANS ABOUT ITS CONNECTION TO SAID FIRST LINKAGE MEANS, A SECOND CYLINDER-PISTON MEANS PIVOTALLY SUPPORTED FROM THE TRUCK AND CONNECTED ADJACENT THE REAR END OF SAID FIRST LINKAGE MEANS AND OPERABLE TO PIVOT SAID FIRST LINKAGE MEANS ABOUT ITS TRUCK SUPPORT WHEREBY TO RAISE AND LOWER CONJOINTLY SAID FIRST AND SECOND LINKAGE MEANS, A SECOND OF PRESSURE FLUID AND CONTROL VALVE MEANS OPERATIVELY CONNECTED TO SAID FIRST AND SECOND LINKAGE MEANS AND RESPONSIVE TO VARIATIONS IN THE ANGLE THEREBETWEEN FOR CONNECTING AND DISCONNECTING SAID SECOND CYLINDER-PISTON MEANS DURING OPERATION THEREOF TO AND FROM SAID PISTON SOURCE OF PRESSURE FLUID WHILE CONNECTING THE FIRST CYLINDER-PISTON MEANS TO SAID SOURCE TO COORDINATE OPERATION OF SAID FIRST AND SECOND CYLINDER-PISTON MEANS IN ORDER TO ELEVATE SAID LOAD ENGAGING MEANS ALONG A PREDETERMINED PATH. 